Not Applicable.
This invention relates spinal cables, and, in particular, a new and improved system including a spinal cable and passer for positioning the spinal cable adjacent a patient""s spine.
Wires and flexible cables have been used for some time to secure fixation devices in the spine when fractures are repaired surgically, and when the spine is straightened or fused. These wires are passed under the lamina of the posterior elements of the vertebra, and then wrapped around a metal rod, or around an adjacent bone structure such as another lamina or a bone graft strut. When tightened, these cables hold the vertebrae rigidly to the fixation device or to each other, and apply forces used to correct deformity or provide rigid fixation to allow healing of fractures and fusions. Other bones are often repaired in the same manner; using cables passed around the bone. In most circumstances the anatomical structures behind the bone are subject to damage if the cable is accidentally passed into the surrounding soft tissue, or if the passer accidentally excoriates or compresses these structures as the cable is passed.
In some areas of the spine, and in certain conditions, the space between the undersurface of the lamina and the dura and spinal cord is very small. Thus, care must be taken so that these structures are not compressed and damaged by the instrument used to pass the cable and by the cable itself during the process of passing it under the lamina. For this reason flexible, multi-wire strand cables are usually preferable to relatively rigid monofilament (or solid) wires. However, passing a flexible cable between the lamina and the dura can be difficult. Heretofore, relatively stiff monofilament lead wires have been attached to the cable ends to facilitate passage of the flexible cable between the lamina and dura. These monofilament wires, however, are not sufficiently stiff to create a reliable pathway between the dura and the undersurface of the lamina, and may fail to pass or else create a false passage into the dura and spinal cord. Moreover, these monofilament lead wires required that the lead wire and the cable be pushed as they were passed under the bone. While these lead wires were stiff, they nevertheless were subject to bending as they were pushed under the bone. If the lead wire or the cable attached thereto would bend during inserting, such bent areas or deformities in the rigid lead wire could compress or damage the dura and/or the spinal cord as they are pushed through the space between the lamina and underlying structures.
In some cases a separate instrument is used to pass the cable or wire between the lamina and dura. These passers are generally tubular structures through which the cable or wire is passed, and therefore are considerably thicker that the cable or wire itself. Use of these prior passers therefore may endanger the spinal cord and dura. One such device is disclosed by U.S. Pat. No. 4,557,259 to Wu in which a series of instruments is described to probe and progressively enlarge the space between the lamina and underlying neural structures and finally allow passage of a tubular device which then allows a wire to be inserted under the lamina. Then the tubular passer is removed.
These problems and restrictions occur, to a varying degree, in all surgical procedures that repair bone with cables passed around the bone structure. Similar conditions exist in cardiovascular surgery during repair of the sternum, and devices have been developed to ensure passage of the fixation band without damage to underlying structures. One such device incorporates a needle attached to a flexible length of suture, which, in turn, is attached to a stiffer and stronger band which itself has a fastener attached to the opposite end. An example of such a device is shown in U.S. Pat. No. 5,089,012 to Prou. The surgical suture disclosed in Prou is stated to be used in open heart surgery for sternotomy closure. This device is unacceptable for use in the spine and around long bones because the plastic strap is too large and bulky to pass safely next to the dura and spinal cord. Also, a needle that is preattached to the device is inconvenient because it will not pass through a conventional cable tensioning device, but instead must be cut off, leaving a loose end (i.e., the wire strands comprising the cable are loose and can begin to unravel) that is difficult to handle.
Passing the flexible cable with a passer that is pushed around the bone or under the lamina is one possible means to solve the problem of passing the cable safely. However, the cable must have a thickness of at least 1.5 mm to achieve adequate strength for general use in the spine and other bone structures. This thickness of cable is often too stiff to grasp and pull under the lamina or around the bone without using an instrument that is too bulky to pass safely in areas with limited space. Such a passer that is pushed under a bone and carries the cable with it is shown in my co-assigned U.S. Pat. No. 5,772,663.
There is a need for a strong and flexible cable that is easy to pass under the lamina or around the bone even in constricted areas, and for a thin passer device that can be passed under the lamina or around the bone with careful surgical control and can pull the cable through without endangering the underlying dura and spinal cord or other structures. The cable must be flexible enough to bend easily without kinking and without compressing the underlying soft tissue structures, but must also be strong and thick enough to function adequately for stabilization of the spine. The passer must be sufficiently rigid to allow firm control while it is being passed under the lamina, but must be sufficiently thin so as to avoid compressing the fragile structures on the other side. The grasping mechanism must also be thin and smooth, and the cable adjacent to the grasping mechanism must not be kinked, so that passing the cable tip does not tear or compress the dura and spinal cord.
Among the objects and features of this invention may be noted the provision of an orthopedic cabling system having a main cable and a flexible lead cable which may be pulled behind (under) a bone with minimal damage or trauma to the tissue or structure behind or under the bone;
The provision of such a cabling system in which the fastener is preattached to the main cable so as to eliminate the need for the surgeon having to handle loose fasteners;
The provision of such a cabling system in which includes a passer which the surgeon may use to pass the cable around or under the bone;
The provision of such a cabling system in which the passer is of a minimal diameter or cross section and yet has sufficient strength and stiffness to enable the passing of the cable around the bone;
The provision of such a cabling system in which the passer is first inserted behind the bone without the cable attached to the passer and, when the end of the passer is accessible to the surgeon on the other side of the bone, permits the cable to attached to the passer and to be pulled under the bone outside of the passer as the surgeon withdraws the passer; and
The provision of such a cabling system which is of economical construction, which is easy for a surgeon to use, which requires little specialized training for a surgeon to use, which securely fastens the cable around the bone while maintaining a desired level of tension in the cable.
Other objects and features of this invention will be in part pointed out and in part described hereinafter.
Briefly stated, a surgical cable and passer system of the present invention comprises a cable assembly including a flexible main cable having a first end and a second end, a thinner and more flexible lead cable attached to one end of the main cable, with the lead cable having a bead affixed to one end of the lead cable. A fastener is preattached to the end of the main cable opposite the lead cable. The cabling system includes a passer having an elongate probe having a thickness less than about three (3) times, and more preferably less than about 2xc2xd times, the diameter of the main cable. The passer probe has a recess therein proximate its distal end and a slot within the passer probe extends from the recess to the free end of the probe. The passer probe is insertable under the bone without the cable so that the free end of the passer is visible on the side of the bone opposite to that from which it was inserted. With the free end of the passer probe accessible on the other side of the bone, the bead on the lead cable is inserted into the recess in the end of the probe and a portion of the lead cable proximate the bead is received within the slot such that at least a portion of the lead cable extends endwise from the probe. With the lead cable so coupled to the passer probe, the surgeon may withdraw the passer probe from under the bone thus pulling the lead cable and the main cable behind the probe. In this manner, the lead cable and the main cable are passed beneath the bone in such manner as to minimize the space required. The fastener preattached to the main cable has a bore therethrough for receiving the free end of the lead cable with the bead thereon and at least a portion of the main cable. The fastener is deformable so as to permanently secure the main cable within the bore while maintaining the desired level of tension on the main cable banded about the bone. A method of passing a cable and permanently banding the cable about the bone with a desired level of tension in the cable is also disclosed.